X-ray equipment



Feb. 6, 1934. w. K. KEARSLEY 1,946,287

X-RAY EQUIPMENT Filed Feb. 21, 193(' Inventor: W i am vK. Kear-s| f by H is At'towngy Patented Feb. 6, 1934 PATENT FFlC-E X-RAY EQUIPMENT William K. Kearsley, Schenectady, N. Y.,-assignor to General Electric Company, a corporation of New York Application FebruaryZl, 1930.- Serial No. 430,418

9 Claims. (c1. 250-34) H The present invention comprises a new combination of X-ray generator, or X-ray tube, and

an electrical supply system therefor, whereby the focusing of the electrons on the anode is automatically controlled during operation to give the most favorable results. This application is a continuation-in-part of my application Serial No. 393,819, filed September 19, 1929 and entitled X-ray equipment.

Heretofore, it has been common practice to so construct X-ray tubes that the impingement of the electrons, or cathode rays, on the anode or target, takes place on a spot of fixed area, the focal spot. Only a certain amount of energy input can be safely used for agiven size of focal spot as otherwise the metal of the anode becomes fused or even vaporized, thereby injuring or even destroying the X-ray tube. To secure sharp definition in radiographs the size of the focal spot must be small. When large X-ray output is desired some sacrifice in definition is re- .quired as a larger focalspot necessarily must be used to avoid overheating. I

As the requirements of the radiographer in definition of radiographs and intensity of X-ray production, are variable, a well-equipped radiographer heretofore kept in stock ready for use several difierent kinds of X-ray tubes, some constructed to operate with a small focal spot and others with a larger focal spot.

- As-a consequence of my invention 1 have provided ail improved X-ray equipment whereby the size of the focal spot is automatically determined so that with an increase in energy the size of the focal spot is increased in corresponding degree and vice versa, thereby always securing for the use of the radiographer the most favorabl'efocusing conditions.

' In accordance with a preferred .embodiment of my invention an electrostatic focusing device in a thermionic X-ray tube is connected to a circuit containing a source of potential which is varied automatically with the energy passing through the X-ray tube so as to control the focusing in the desired manner.

-' My invention will be described in detail in the following specification taken together with the accompanying drawing and its novel features pointed out in theappended claims.

Fig. 1 of the drawing is a diagram of a preferred embodiment of my invention which includes. a thermionic vacuum tube connected in such manner to an X-ray tube that a variable potential across the vacuum tube is impressed upon the focusing member of theX-ray'tube;

Fig. 2 illustrates a modification and Fig. 3 isfa detailed view showing in section a cathode portion'of-a vacuum tube'constructedto operate in accordance with my invention."

In the system shown in Fig. 1 there is included anX-ray-tube or generator comprising a bulb'l having oppositely extending electrode arms and containing an anode 2 and a cathode 3 (here shown diagrammatically) which do not differ essentially in construction fromthe electrodes ordinarily employed in a well-known form of thermionic X ra'y tubes. The anode comprises a mass of highly refractory metal, preferably tungsten; The anode stem 4 is sealed into a support 5 of the usual construction. The cathode, as best 7 shown in Fig. 3, comprises a spiral filament 6, also preferably consisting of tungsten. This filament is connected at one 'end'to a conductor 7 and at its opposite'end tofa ring 8, carried by a conductor 9. The cathode conductors are sealed into a stem 10 and lead to external contact'devices (not shown). Surrounding thecathode filament 6 is a focusing device consisting of-a dished tubular member 11 which is supported by the' conductors '12, 12, in turn mountedupon a split metal tube 13 carried by the glass tube 14 which forms with the stem 10 a reentrant member in the cathode arm of the envelope.- Aconductor 15 contacting with thetube 13 is'se aled through the envelope of theX-ray tube-to an external circuit described hereinafter.

The cathode conductors '7, -9 are connected by I thewireslfi, 1'! (Fig.1) to the secondary'winding 18 of a transformer 19, whereby heatingcurrent is'supplied to maintain the cathode at an j electron-emitting temperature. Current for gerierating X-rays'is supplied by the high potential secondary winding of a main transformer '20 through a rectifier or mechanicaltranslator' 21 ofany' suitable and well-known type. Both the transformers 19 and 20 derive energy for their primary windings from the alternating current mains 22. The supply circuit'23 of the trans- "former 19 contains an adjustable resistor 24.

The supply circuit '25 of the transformer 20 contains a switch conventionally indicated at 26. A vacuum tube 27 is included in circuit between the transformer 20 and the'cathode filament 6,

by conductors 31, 15, 34 m the one-hand and conductors 28, 1'7, 9 on the other hand. The cathode 30 of the tube'2'7 is connected by the conductors 31, 31' to the secondary winding 32 which may be wound on the coreof thetrans- "former 19' in common with 'thewinding 18,0r Iconne'cted'in any suitablemanner' to be respo'ri- 1N thermionic vacuum tube varies inversely with the temperature of the cathode up to the saturation value of the cathode electron emission. The negative bias which is given to the focusing member 11 by the connection of the circuit 15, 28, containing the vacuum tube 27, to this member is made high enough to cause a convergence or focusing of the cathode rays upon the focal spot of the most favorable area for anX-ray generat ing current at the lower limit of the operating range of the X-ray tube. When a higher operating current is desired for the X-ray tube, the temperature of the cathode 6 must be increased. This is accomplished by decreasing the resistance 24 in the primary circuit of the transformer 19 thereby simultaneously increasing the temperature of the filament 30 of the vacuum tube 27 and lowering the voltage drop in the vacuum tube. The negative bias of the focusing member is decreased by the lowering of the voltage drop in the vacuum tube, and, therefore, with the greater energy input in the X-ray tube the focal spot is automatically enlarged. By proper proportion- ,ing of the resistor 33 in the cathode circuit of the tube 27 and by adapting the geometry of the X- ray tube and the vacuum tube with respect to the electron emissivity of their cathode filaments, the increase in area of the focal spot may be caused to keep step with an increase in current through the X-ray tube so as to always secure the most favorable focal spot with any given energy input. In order further to adapt the'constants of the vacuum tube 27 to those of theX-ray gtu be so as to obtain an accurate change of size of the focal spot corresponding to the change in currentpassing through the X-ray tube, it may be desirable to insert a permanent resistance 29 in the line 28.

. The system shown in Fig. 2 is similar to the sys tem shown in Fig. 1 but in addition to-currentresponsive means there is provided means for controlling the size of the focal spot to respond to changes of voltage of the energy supply of the X-ray tube. Referring to this figure, a transformer .60 is provided which cooperates with the transformer 32 in heating the filament 30. The

winding 18 which supplies current to heat the filament of the X-ray tube must not receive changes in voltage due to fluctuations of line voltage as in such case the current through the X-ray tube would vary irregularly with line voltagel A stabilizer, as represented by the resistor' hence is provided.

The X-ray tube, however, responds to variations of line voltage in the intensity or hardness of the X-ray produced therein accompanied by variations in heat evolution at the focal spot. The area of the focal spot is varied accordingly by the folondary winding of the transformer 60 is connected by the conductors 31, 31 in series with the secondary winding 32, the windings being connected .bination of a source of energy,

When a rise or fall of potential occurs in the mains 22, a corresponding rise or fall of current occurs in the circuit 31, 31, causing the electron emissivity of the filament 30 to correspondingly vary. For example, an increase of voltage increases the electron emission of the filament 30. This decreases the potential drop across the tube 27. The fall of potential between the focusing member 11 and the cathode 6 broadens the focal spot, thus privides a greater surface for the increased energy of bombardment of the anode. Upon a fall of voltage the converse action takes place, the focal spot being sharpened. The size of the focal spot thus is controlled in response to changes of energy.

What I claim asnew and desire to secure by Letters Patent of the United States, is,

1. The combination of an X-ray tube having main electrodes including'a thermionic cathode, a main transformer connected to operate said tube, means for focusing the X-ray producing discharge in said tube, an auxiliary thermionic tube connected in series with said X-ray tube, a conductive connection between said focusing means and said auxiliary tube, a second transformer having secondary windings connected respectively 'to the cathode of said X-ray tube and the cathode of said auxiliary tube, a common primary winding for said second transformer and a third transformer to assist one another.

having a primary winding connected in circuit with said main transformer and a secondary winding connected in circuit with the cathode of said auxiliary tube.

2. An electrical'discharge apparatus comprising thecombination of a main discharge tube, the parts of which include a cathode, an anode, and a device whereby the focusing of a discharge upon the anode may be varied, a main electrical supply circuit connected to the cathode and anode of said main tube, an auxiliary discharge tube connected in series with said main tube in said supply circuit, and a conductor connecting the focusing device of said main tube to said auxiliary tube whereby the field of the focusing device and hence the focus of the discharge is varied in accordance with the drop of potential in said auxiliary tube.

{one of the electrodes of said vacuum tube. r 4. An X-ray apparatus comprising the combination of a source of energy, an X-ray tube having an anode, a thermionic cathode, and a focusing member surrounding said cathode, a main circuit connecting said-source and the anode and cathode of said X-ray tube, a regulating vacuum tube in said main circuit connected between said source and the cathode of-said X-ray tube, and an electrical conductor connecting the cathode of said regulating tube and the focusing member of said -ray tube. j

5. An X-ray apparatus comprising the coman X ray tube having an anode, a thermionic cathode and a focusing member surrounding said cathode, a main circuit connecting said source and the anode and cathode of said X-ray tube, a regulating vacuum tube in said main circuit connected between said source and the cathode of said X-ray .tube, .an electrical conductor connecting one of the electrodes of said regulating tube and the focusing member of said X-ray tube, and means for simultaneously varying the electron emission of the respective cathodes of said X-ray tube and said regulating tube.

6. An electrical apparatus comprising the combination of a main source of energy, a main discharge tube having an anode, a thermionic cathode and a focusing member surrounding said cathode, a supply circuit connecting said source to the anode and cathode of said main discharge tube, a regulating discharge tube in said circuit connected between said source and the cathode of said main tube, an electrical circuit connecting said. focusing member and the cathode of said auxiliary device, and a transformer having secondary windings, one of which is connected to supply the cathode of said main tube, and another of which is being connected to supply the cathode of said auxiliary tube.

7. An electrical discharge apparatus comprising the combination of a main discharge tube, the parts of which include a cathode, an anode, and a device whereby the focus of a discharge upon the anode may be varied, a main electrical supply circuit connected to the cathode and anode of said main tube, an auxiliary discharge tube connected in series with said main tube, a conductor connecting the focusing device of said main tube to said auxiliary tube whereby the focus of the main discharge is varied in accordance with the drop of potential in said auxiliary tube, a heating circuit for the cathode of said auxiliary tube, means for varying the current in said heating circuit in response to variations of potential of said main supply circuit, and common means for varying the electron emission of the cathode of said main tube and the cathode of said auxiliary tube.

8. An X-ray apparatus comprising the combination of an X-ray tube having main electrodes, including a thermionic cathode and a focusing device, a thermionic regulating tube connected in series with one of said electrodes, a conductor connecting the focusing device of said X-ray tube to one of the electrodes of said regulating tube, a transformer having a primary winding and a plurality of secondary windings connected respectively to supply the cathodes of said X-ray tube and said regulating tube, a main transformer having a secondary winding connected to supply energy to said X-ray tube, and a transformer having a primary winding connected in series with the primary winding of said main transformer and a secondary winding connected in circuit with the transformer winding which supplies the cathode of said regulating tube.

9. The combination of a main thermionic device, means for focusing electrons emanating from the cathode of said device, a supply circuit for said device, an auxiliary thermionic device connected in series with said main device in said circuit, a conductor connecting said focusing means to an electrode of said auxiliary device, common means for maintaining at an operating temperature the cathodes of both the main and the auxiliary thermionic devices, and means for varying the temperature of the cathode of said auxiliary device in response to variations of voltage in the supply circuit of said main device thereby varying the potential of said focusing means and sharpening or broadening the focus of a discharge in said main device in response to variations of space current therein.

WILLIAM K. KEARSLEY. 

